1. Field of the Invention
The present invention relates to a hydrogen storage electrode for use as an anode of an alkaline battery, and also to a process for producing the same.
2. Description of the Prior Art
Process for producing a hydrogen storage electrode can be grouped roughly into two methods according to whether or not sintering is applied in the process. Namely, one is sintering method as described, e.g., in Publication of Unexamined Japanese Patent Application No. 1-132048 (1989), according to which hydrogen storage alloy powder set in contact with an electric current collector is bonded together by sintering under a temperature of about 1,000.degree. C. while the former alloy powder is held pressed against the latter current collector.
The other is non-sintering method as disclosed, e.g., by Publications of Unexamined Japanese Patent Applications No. 2-278659 (1990) and No. 3-98261 (1991). According to this method, hydrogen storage alloy powder is mixed with copper powder which amounts to about as many as 4 to 5 times by weight as the alloy powder and serves as a conductivity aid, and the mixture is pressed onto a current collector for bonding thereby to form a hydrogen storage electrode. Alternatively, the mixture of the hydrogen storage alloy powder and the conductivity aid may be mixed further with a binder such as fluororesin powder and then pressed and bonded to a current collector in the atmosphere of about 300.degree..
It is noted, however, that the production process according to the sintering method is complicated and hence costly and also that the hydrogen storage electrode made in the non-sintering method is poor not only in conductivity, but also in the mechanical bonding strength between particles of the hydrogen storage alloy powder and also between the alloy powder and the current collector.
According to the non-sintering method in which a large amount of conductivity aid is used, discharge capacity per given weight or volume of the resulting electrode will be reduced, and the use of fluororesin as a binder will increase the internal electrical resistance of the electrode. If only a less amount of binder is added with an attempt to prevent such an increase of the resistance, it will affect the mechanical bonding strength and hence the charge and discharge cycle life of the electrode. Additional heating to a substantially high temperature may be performed to secure the bonding strength, but only at the sacrifice of additional cost.